Three‐point bending tests. Part II: An improved formula for the modulus of rupture and numerical simulations

The goal of this paper is to analyze analytical and numerically, from several perspectives, the modulus of rupture (MOR) for brittle materials, studying the bending test of three points which is normally used in laboratory to calculate it. In particular, we will give four different approaches to the MOR: through the classical theory of beams; by means of the one‐ and three‐dimensional numerical simulations; and by using an improved expression to the MOR obtained through its asymptotic analysis. Finally, we will present these methodologies for cylindrical and rectangular beams made of porcelain. Copyright © 2011 John Wiley & Sons, Ltd.     

广义f-投影算子的稳定性及其应用

在Banach空间中,本文研究广义f-投影算子关于集合扰动的稳定性.作为应用,本文在Banach空间中运用广义f-投影算子解决了一类广义变分不等式问题.     

High-pressure and high-temperature bulk modulus of cubic fluorite-type MgF2 from quasi-harmonic Debye model

A detailed theoretical study of the isothermal and adiabatic bulk moduli of MgF₂ with a fluorite structure under high pressure and temperature has been carried out by means of first-principles density functional theory calculations combined with the quasi-harmonic Debye model in which the phononic effects are considered. Particular attention is paid to the prediction of the isothermal bulk modulus and its first and second pressure derivatives for the first time. The calculated ground state properties agree well with other theoretical values. At extended pressure and temperature ranges, the variation of the bulk modulus which plays a central role in the formulation of approximate equations of state has also been predicted. The properties of MgF₂ with a fluorite structure are summarized in the pressure range of 0–135 GPa and the temperature up to melting temperature 1500 K.     

Mechanical properties of superhard diamondlike BC5

Using first-principles calculations, we systematically studied the mechanical properties and electronic structure of the recently synthesized diamondlike BC₅. Our calculated bulk modulus B, shear modulus G, elastic constant c₄₄, and theoretical hardness H confirm that BC₅ is an ultraincompressible and superhard material. Also, it exhibits mechanical stability and metallic features. Electronic structures show that a strong covalent bond network through sp³ hybridization is the origin of the excellent mechanical properties of BC₅. Our results show that BC₅ has good prospects in electronic application as a superhard material.     

Calculation of anisotropic properties of dental enamel from synchrotron data

Obtaining information about the intrinsic structure of polycrystalline materials is of prime importance owing to the anisotropic behaviour of individual crystallites. Grain orientation and its statistical distribution, i.e. the texture, have an important influence on the material properties. Crystallographic orientations play an important role in all kinds of polycrystalline materials such as metallic, geological and biological. Using synchrotron diffraction techniques the texture can be measured with high local and angular resolving power. Here methods are presented which allow the spatial orientation of the crystallites to be determined and information about the anisotropy of mechanical properties, such as elastic modulus or thermal expansion, to obtained. The methods are adapted to all crystal and several sample symmetries as well as to different phases, for example with overlapping diffraction peaks. To demonstrate the abilities of the methods, human dental enamel has been chosen, showing even overlapping diffraction peaks. Likewise it is of special interest to learn more about the orientation and anisotropic properties of dental enamel, since only basic information is available up to now. The texture of enamel has been found to be a tilted fibre texture of high strength (up to 12.5×). The calculated elastic modulus is up to 155 GPa and the thermal expansion up to 22.3 × 10^?6 °C^?1.     

Effects of pressure and temperature on the isothermal bulk modulus of CaO

Molecular dynamics (MD) simulations have been performed to investigate the effects of pressure and temperature on the isothermal bulk modulus of CaO using pair-wise interactions that include polarization effects through the shell model (SM). The dependence of isothermal bulk modulus B_T of CaO on the compression ratio V/V₀ and pressure P have been obtained from MD runs at T=300 K, and compared with the available experimental data and other theoretical results. A good agreement between theory and experiment is obtained. Meanwhile, B_T dependence on temperature T at zero pressure is investigated. At extended pressure and temperature ranges, SM-MD method has also been carried out for predicting the P-V-T equation of state and isothermal bulk modulus at different temperatures along the isotherms 0, 1000, 2000, 3000, and 4000 K, and at different pressures along the isobars 5, 15, 30, 40, and 50 GPa for CaO, respectively.     

pH响应型P(HEMA/MAA)纳米微凝胶分散液的凝胶化行为和流变性能

制备了在修复受损组织方面有应用潜能的纳米级聚(甲基丙烯酸羟乙酯/甲基丙烯酸) (P(HEMA/MAA))微凝胶; 采用试管倒转法对不同pH值和浓度的P(HEMA/MAA)微凝胶分散液的凝胶化相转变行为进行了研究; 借助椎板流变仪考察了低浓度和高浓度微凝胶分散液的流变性能, 并对pH触发物理凝胶化相转变机理进行了推测. 结果表明: 在生理pH值环境下, 一定浓度的P(HEMA/MAA)微凝胶分散液可以发生凝胶化相转变形成凝胶态, pH=7时, HEMA/MAA进料摩尔比为8/2的微凝胶分散液凝胶化后得到的凝胶力学性能最佳, 最大弹性模量(G')可达7.58×10³ Pa; P(HEMA/MAA)微凝胶颗粒在不同条件下具有不同的溶胀效果, 导致低浓度分散液的表观粘度发生相应的变化, 并由此推测出微凝胶颗粒的溶胀过程由外及内, 分为三个阶段; 高浓度微凝胶分散液发生凝胶化相转变主要是由颗粒间或颗粒与分散介质间形成的空间静电稳定作用和氢键共同作用引起的.     

Uniqueness in determining a sound-hard ball with the modulus of a far-field datum

In this paper, various original properties of the Bessel and spherical Bessel functions are presented, based on which we prove a novel uniqueness result of an inverse acoustic obstacle scattering problem, that is, a sound-hard ball with a known center can be uniquely determined by the modulus of a single far-field datum corresponding to a single incident plane wave.     

A new class of generalized f-projected dynamical system in Banach spaces

In this article, a new class of generalized f-projected dynamical systems is introduced and studied in Banach spaces. A global existence and uniqueness result of generalized f-projected dynamical system is proved, which generalizes the existence result of Xia and Vincent [Y.S. Xia and T.L. Vincent, On the stability of global projected dynamical systems, J. Optim. Theory Appl. 106 (2009), pp. 129–150]. The global convergence stability of the generalized f-projected dynamical system and the sensitivity result of solutions set with perturbations of the constraint sets are also obtained under some suitable conditions.     

Square‐Micrometer‐Sized,Free‐Standing Organometallic Sheets and Their Square‐Centimeter‐Sized Multilayers on Solid Substrates

Oligofunctional terpyridine‐based monomers are spread at an air/water interface, where they are connected with transition metal salts such as Fe(II) into mechanically coherent monolayer sheets of macroscopic dimension. The conversions of these processes are determined by XPS for several monomer/metal ion combinations. The sheets are transferred onto TEM grids, the 20 × 20 square micrometer sized holes of which can be spanned. AFM indentation experiments provide in‐plane elastic moduli which are compared with naturally occurring sheets such as graphene. The new organometallic sheets are also used to create multilayer assemblies on square centimeter length scales on solid substrates. Finally some directions are provided where this research can lead to in future and where its application potential lies.